Various methods have been used to connect plastic tubing in fluid-tight connection with other plastic parts, such as plastic fluid couplings or hubs used in medical devices such as catheters. Plastic tubes for intravenous catheter placement units or infusion sets, for example, are necessarily of small size since they are to be placed in a patient's vein for infusion purposes. The tube must be connected to a hub or other coupling that can be connected with a source of infusion liquid. The connection between the plastic tube and the hub must, of course, be fluid-tight as well as mechanically strong, and it must remain so throughout its use. Should the catheter tube become completely disconnected from its hub during use, it could move into the patient's vein. If a fluid leak occurs at the connection, the patient will receive less infusion liquid than intended and the liquid would flow outside the infusion system.
Because such tubing often has small inner and outer diameters, and must be made of a material which is substantially inert to the body, problems of obtaining a good mechanically strong connection, as well as a good fluid-tight connection with a plastic hub, which hub may be of a different material, have occurred. Also, certain tube materials may be of a type which do not chemically bond to the plastic material of the hub.
In some cases, sliding members or threaded coupling members are moved together to clamp a tube in place, and in some cases, a metal or plastic ferrule may be used. In U.S. Pat. No. 3,720,210, a tube of polytetrafluoroethylene, known under the trademark Teflon, is provided with an integral flange at one end and an additional outer tubular member or sleeve of a different plastic material, and the tube end and sleeve are insert molded in a hub member. However, such a method requires the use of the additional sleeve member. Also, in use, the tube may tend to rotate on its axis relative to the hub and this may result in the leaking of fluid from the system.